Streamwise fences for the reduction of trailing-edge noise in a NACA633018 airfoil

Streamwise fences for the reduction of the trailing-edge noise are experimentally investigated on a NACA633018 airfoil. Interchangeable trailing-edge inserts with streamwise fences of different spacing and height are tested in an anechoic wind tunnel. Far-field trailing-edge noise was measured by an array of microphone and the airfoil drag was calculated from the wake profiles acquired by a wake rake. The transversal spacing between the fences has a much stronger impact on noise reduction than the fences height. A maximum noise reduction of 5-6dB is obtained from fences having a spacing of 2 mm, and it is achieved in the range of Strouhal numbers based on the chord of 15-40, equivalent to frequencies 1-3 kHz. When increasing the spacing between the fences from 2 mm to 4 mm, a different aeroacoustic behavior is observed, with a lower noise reduction at high frequencies, and a higher noise reduction and low frequencies. Increasing the angle of attack from α=0° to α=6° does not lead to any significant deterioration of the noise reduction performance. From a wake survey, the coefficient of drag was found to increase of only 6-7%when installing trailing-edge inserts with fences.